Note: Descriptions are shown in the official language in which they were submitted.
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CONTACT VALVE TRAY FOR A MASS TRANSFER COLUMN
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to columns in which mass
transfer and heat
exchange occur and, more particularly, to contact trays for use in such
columns to facilitate
interaction between fluid streams flowing within the columns.
[0002] As used herein, the term "mass transfer column" refers to a column
in which mass
transfer and/or heat exchange occur. Examples of mass transfer columns include
distillation,
absorption, stripping, and extraction columns.
[0003] Various types of trays are commonly used in mass transfer columns to
promote
contact and mass transfer between ascending and downwardly flowing fluid
streams. The
ascending fluid is typically vapor and the descending fluid is typically
liquid, although liquid-
liquid and gas-liquid systems are also known. Each tray normally extends
horizontally across
substantially the entire horizontal cross section of the column and is
supported around its
perimeter by a ring welded to the inner surface of the circular column wall or
shell. A number of
trays are positioned in this manner with a uniform vertical spacing between
adjacent trays. The
trays may be located in only a portion of the column to perform one part of a
multi-step process
occurring with the column. Alternatively, the trays may fill substantially the
entire open area
within the column.
[0004] Trays of the type described above contain one or more downcomers
that are
positioned at openings in the tray deck to provide passageways for liquid to
descend from one
tray to an adjacent lower tray. Prior to entering the downcomer, the liquid on
the tray deck
interacts with ascending vapor that passes through openings provided in
selected portions of the
tray deck. Those areas of the tray deck containing vapor openings are commonly
referred to as
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"active" areas because of the vapor and liquid mixing and frothing that occurs
above those areas
of the tray.
[0005] The vapor openings in the tray deck can be simple sieve holes or can
be formed as
part of fixed or moveable valves. Conventional valves have valve covers
supported over the
opening in the tray deck by attachment legs. In fixed valves, the valve cover
is fixed against
vertical movement. In moveable valves, the valve cover is able to move up and
down in
response to variations in vapor or fluid flow rates through the opening. The
valve cover
functions to shield the opening in both the fixed and moveable valves against
undesirable
weeping of fluid downwardly through the opening and to laterally direct the
vapor or other fluid
that has ascended through the opening for enhanced interaction with the fluid
flowing along the
tray deck. While a variety of fixed and moveable valves are known, further
improvements in
their design and performance are desired.
SUMMARY OF THE INVENTION
[0006] In one aspect, the present invention is directed to a contact tray
for use in a mass
transfer column. The contact tray comprises a generally planar tray deck and a
plurality of
valves distributed across the tray deck. Each of the valves comprises an
opening that extends
through the tray deck to allow for passage of fluid through the tray deck, a
weir extending
upwardly from the tray deck around a perimeter of the opening, and a valve
cover supported by
attachment legs above said opening and said weir. The valve cover extends
outwardly beyond
the entire perimeter of the opening and has a downwardly extending perimeter
region.
[0007] In another aspect, the present invention is directed to a contact
tray for use in a mass
transfer column. The contact tray comprises a generally planar tray deck and a
plurality of
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valves distributed across the tray deck. Each of the valves comprises an
opening that extends
through the tray deck to allow for passage of fluid through the tray deck, a
weir extending
upwardly from the tray deck around an entire perimeter of the opening, a valve
cover supported
above said opening and said weir by first and second attachment legs
positioned at opposite ends
of said valve cover, and a vent opening formed in one of said attachment legs.
The valve cover
extends outwardly beyond the entire perimeter of the opening and has a
downwardly extending
perimeter region.
[0008] In a further aspect, the present invention is directed to a contact
tray for use in a mass
transfer column. The contact tray comprises a generally planar tray deck and a
plurality of
valves distributed across the tray deck. Each of the valves comprises an
opening that extends
through the tray deck to allow for passage of fluid through the tray deck, a
weir extending
upwardly from the tray deck around an entire perimeter of the opening, a valve
cover supported
above said opening and said weir by first and second attachment legs
positioned at opposite ends
of said valve cover, and a vent opening formed in one of said attachment legs.
The opening in
the tray deck is circular and the valve cover is in the form of an isosceles
trapezoid. The
attachment legs comprise first and second attachment legs respectively
connected to opposed
parallel first and second ends of the valve cover. The valve cover each
extends outwardly
beyond the entire perimeter of the opening in the tray deck and the first
attachment leg has a
width greater than a largest width of the opening. The valve cover has a
downwardly extending
perimeter region.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0009] In the accompanying drawings that form part of the specification and
in which like
reference numerals are used to indicate like components in the various views:
[00010] Fig. 1 is a fragmentary, perspective view of a column in which mass
transfer and/or
heat exchange are intended to occur and in which a portion of a shell of the
column is broken
away to show one embodiment of fixed valve contact trays of the present
invention;
[00011] Fig. 2 is an enlarged, perspective view of the contact trays in the
column shown in
Fig. 1;
[00012] Fig. 3 is a fragmentary, perspective and partially exploded view of
one of the contact
trays of Figs. 1 and 2, showing fixed valves of the contact tray on a further
enlarged scale with
one of the valve covers removed to show details of construction;
[00013] Fig. 4 is a fragmentary, side elevation view of one of the contact
trays showing two of
the fixed valves taken in vertical section along line 4-4 of Fig. 3 in the
direction of the arrows;
[00014] Fig. 5 is a top perspective view of one of the valve covers for the
fixed valve;
[00015] Fig. 6 is a bottom perspective view of the valve cover shown in Fig.
5;
[00016] Fig. 7 is an end elevation view of the valve cover shown in Fig. 5
taken in the
direction from a second end to a first end of the valve cover;
[00017] Fig. 8 is a side elevation view of the valve cover shown in Fig. 5;
[00018] Fig. 9 is an end elevation view of the valve cover shown from the
opposite end of the
view in Fig. 7;
[00019] Fig. 10 is a top plan view of the valve cover shown in Fig. 5;
[00020] Fig. 11 is a bottom plan view of the valve cover shown in Fig. 5;
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[00021] Fig. 12 is a fragmentary, perspective and partially exploded view of
another
embodiment of one of the contact trays containing moveable valves with one of
the valve covers
being removed to show details of construction;
[00022] Fig. 13 is a fragmentary, elevation view of the contact tray of Fig.
12 showing two of
the moveable valves taken in vertical section along line 13-13 of Fig. 12 in
the direction of the
arrows;
[00023] Fig. 14 is a fragmentary, side elevation view of one of the contact
trays showing two
of the moveable valves taken in vertical section along line 4-4 of Fig. 3 in
the direction of the
arrows;
[00024] Fig. 15 is a top perspective view of one of the valve covers for the
moveable valve;
[00025] Fig. 16 is a bottom perspective view of the valve cover shown in Fig.
15;
[00026] Fig. 17 is an end elevation view of the valve cover shown in Fig. 15
taken in the
direction from a second end to a first end of the valve cover;
[00027] Fig. 18 is a side elevation view of the valve cover shown in Fig. 15;
[00028] Fig. 19 is an end elevation view of the valve cover shown from the
opposite end of
the view in Fig. 17;
[00029] Fig. 20 is a top plan view of the valve cover shown in Fig. 15; and
[00030] Fig 21 is a graph showing the comparative performance of a fixed valve
contact tray
of the present invention against a fixed valve contact tray lacking the
inventive features.
DETAILED DESCRIPTION
[00031] Turning now to the drawings in greater detail and initially to Fig.
1, a mass transfer
column suitable for use in mass transfer or heat exchange processes is
represented generally by
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the numeral 10. The column 10 may include an upright, external shell 12 that
may be generally
cylindrical in configuration, although other configurations, including
polygonal, are possible and
are within the scope of the present invention. The shell 12 may be of any
suitable diameter and
height and may be constructed from one or more rigid materials that are
desirably inert to, or are
otherwise compatible with, the fluids and conditions present during operation
of the column 10.
[00032] The column 10 may be of a type used for processing fluid streams,
typically liquid or
vapor streams, to obtain fractionation products or to otherwise cause mass
transfer or heat
exchange between the fluid streams. For example, the column 10 may be one in
which crude
atmospheric, lube vacuum, crude vacuum, fluid or thermal cracking
fractionating, coker or
visbreaker fractionating, coke scrubbing, reactor off-gas scrubbing, gas
quenching, edible oil
deodorization, pollution control scrubbing, or other processes occur.
[00033] The shell 12 of the column 10 defines an open internal region 14 in
which the desired
mass transfer or heat exchange between the fluid streams occurs. In one
implementation, the
fluid streams may comprise one or more ascending vapor streams and one or more
descending
liquid streams. In other implementations, the fluid streams may comprise
substantially any
combination of ascending or descending liquid streams or ascending or
descending vapor
streams.
[00034] One or more fluid streams may be directed into the column 10 through
any number of
feed lines 16, such as lower feed lines 16a or upper feed lines 16b,
positioned at appropriate
locations along the height of the column 10. In one implementation, vapor
streams may be
generated within the column 10 rather than being introduced into the column 10
through the feed
lines 16a, 16b. One or more fluid streams may be directed out of the column 10
through any
number of takeoff lines 18, such as lower takeoff line 18a and upper takeoff
line 18b. In one
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implementation, liquid may be introduced through upper feed line 16b, descend
through the
column 10, and be removed through lower takeoff line 18a, while vapor may be
introduced
through lower feed line 16a, ascend through the column 10, and be removed
through upper
takeoff line 18b.
[00035] Other column components that would typically be present, such as
reflux stream
lines, reboilers, condensers, vapor horns, liquid distributors, and the like,
are not illustrated in the
figures because they are conventional in nature and an illustration of these
components is not
believed to be necessary for an understanding of the present invention.
[00036] In accordance with the present invention, a plurality of pairs of
fixed-valve contact
trays 20 and 22 is positioned within the open internal region 14 of the column
10 to facilitate
interaction of the fluids flowing within the open internal region 14. The
trays 20 and 22 extend
generally horizontally across the entire cross-section of the column 10 and
are arranged in an
alternating fashion such that each tray 20 overlies and is vertically adjacent
to one of the trays
22. The specific design of each tray 20 and 22 can be varied while remaining
within the scope of
the present invention.
[00037] In the illustrated embodiment of Figs. 1-2, the trays 20 and 22 are
constructed to form
a single-pass fluid flow arrangement in which the descending fluid flows from
end-to-end
opposite flow directions on each tray 20 and 22. Each tray 20 has a side
downcomer 24 that is
positioned at one end of a tray deck 26 that is normally formed from
interconnected tray panels.
The side downcomer 24 receives and removes the descending fluid from the tray
deck 26 and
delivers it to one end of a tray deck 28 of a paired underlying tray 22. The
fluid then flows
across the tray deck 28 in an opposite direction to a side downcomer 30 that
is positioned at an
opposite end of the tray deck 28. The fluid enters the side downcomer 30 and
is delivered to the
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tray deck 26 of the next underlying tray 20. This flow pattern is repeated on
each of the lower
pairs of trays 20 and 22. Although the trays 20 and 22 are illustrated as
being constructed for
single-pass fluid flow, the invention encompasses trays constructed for multi-
pass flow.
[00038] Fixed valves 32 are positioned in a preselected pattern on some
portions of the tray
decks 26 and 28 of the trays 20 and 22 to allow vapor or another fluid to
ascend through the tray
decks 26 and 28 and interact with flowing across the upper surface of the tray
decks 26 and 28.
The area of the tray decks 26 and 28 containing these fixed valves 32 is
normally referred to as
the active area of the trays 20 and 22.
[00039] The area of the tray deck 28 underlying the side downcomer 24 of the
overlying tray
20 comprises an inlet panel 34 and is normally imperforate or has shielded
flow passages that
impede or prevent the descending fluid from passing through the inlet panel
34. Similarly, the
area of the tray deck 26 underlying the side downcomer 30 of the overlying
tray 22 comprises an
inlet panel 36 that is imperforate or has shielded flow passages.
[00040] The side downcomer 24 of each tray 20 comprises a wall 38 that extends
in a chordal
fashion across the open internal region 14 of the column 10. The upper portion
of the wall 38, or
a separate piece attached to the wall 38, extends upwardly above the tray deck
26 to form an inlet
weir 40 that causes liquid to accumulate on the tray deck 26 before spilling
over the weir 40 and
entering the side downcomer 24. A lower portion of the wall 38 is spaced above
the underlying
tray deck 28 or contains flow openings (not shown) to allow fluid to exit the
side downcomer 24
and flow along the upper surface of the tray deck 28 before entering the side
downcomer 30 at
the opposite end of the tray deck 26.
[00041] Similarly, the side downcomer 30 on each tray 22 comprises a chordal
wall 42 that
has a lower portion that is spaced above the underlying tray deck 26 or
contains flow openings
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(not shown) to allow fluid the exit the side downcomer 30 and flow along the
upper surface of
the tray deck 26. An upper portion of the wall 42, or a separate piece
attached to the wall 42,
extends upwardly above the tray deck 28 to form an inlet weir 44. While each
of walls 38 and
42 is illustrated as planar and vertically-extending, stepped, sloped or multi-
chordal walls or
other constructions are within the scope of the invention.
[00042] Turning now to Figs. 3-11, each of the fixed valves 32 on tray deck 26
comprises an
opening 46 that extends through the tray deck 26 to allow for passage of fluid
through the tray
deck 26 and a weir 48 extending upwardly from the tray deck 26 a preselected
distance along an
entire perimeter of the opening 46. Each fixed valve 32 also includes a valve
cover 50 supported
by first and second attachment legs 52 and 54 at a fixed, preselected location
above the opening
46. While two attachment legs 52 and 54 are used in the illustrated embodiment
to support the
valve cover 48, additional attachment legs could be used if desired.
[00043] The attachment legs 52 and 54 in the illustrated embodiment extend
upwardly from
the tray deck 26 and are located at opposite ends of the valve cover 50. The
attachment legs 52
and 54 are shown as extending generally perpendicularly to the tray deck 26,
but they may in
other embodiments slope toward or away from each other. Each of the attachment
legs 52 and
54 has an upper end that is attached to and is integral with an edge of the
valve cover 50.
[00044] The attachment legs 52 and 54 are fixed to the tray deck 26 in a
suitable fashion. In
the illustrated embodiment, the attachment legs 52 and 54 extend downwardly
through parallel
slots 56 and 58 (Fig. 3), respectively, positioned on opposite sides of the
opening 46 in the tray
deck 26. Each of the attachment legs 52 and 54 includes a pair of shoulders 60
and 62,
respectively, that engage against an upper surface of the tray deck 26 and a
locking tab 64 that
has an upper surface spaced a preselected distance below the shoulders 60 and
62. The locking
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tab 64 engages against an under surface of said tray deck 26. The distance
between the shoulders
60 and 62 and the upper surface of the tab 64 is selected to prevent vertical
movement of the
attachment legs 60 and 62, and valve cover 50 carried thereon, when the
shoulders 60 and 62 of
the attachment legs 52 and 54 engage the upper surface of the tray deck 26 and
the upper
surfaces of said locking tabs 64 engage against the under surface of the tray
deck 26. If desired,
the distance between the shoulders 60 and 62 and the upper surface of the
locking tab 64 can be
increased to allow some vertical movement of the attachment legs 52 and 54 and
valve cover 50
in response to variations in upward pressure exerted on the under surface of
the valve cover 50
by the fluid ascending through the openings 46 in the tray deck 26.
[00045] The locking tab 64 can be of various suitable forms that allow the
attachments legs 52
and 54 to be inserted downwardly through the slots 56 and 58 before the upper
surface of the
locking tab 64 is positioned to engage against an under surface of the tray
deck 26. For example,
the locking tab 64 can simply be manually bent to bring its upper surface into
engagement with
the under surface of the tray deck 26 following installation of the attachment
legs 52 and 54. In
the illustrated embodiment, the locking tab 64 is formed in the associated
attachment leg 52 or
54 by cutting along two sides and an upper edge of the locking tab 64 while
leaving a lower edge
of the locking tab 64 attached to the attachment leg 52 or 54. The locking tab
64 is then bent
about the attached lower edge to move the remainder of the locking tab 64 out
of the plane of the
associated attachment leg 52 or 54. When the attachment leg 52 or 54 is
inserted downwardly
through the associated slot 56 or 58, the portions of the tray deck 26
surrounding the slot 56 or
58 cause the locking tab 64 to pivot toward the plane of the attachment leg 52
or 54. The locking
tab 64 then springs outwardly once the locking tab 64 clears the slot 56 or
58.
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[00046] Attachment leg 52 has a width that is greater than a largest
corresponding width of
the opening 46 in the tray deck 26 to shield the opening 46 against unwanted
weeping of fluid
downwardly through the opening 46. The fixed valve 32 is oriented on the tray
deck 26 so that
the attachment legs 52 and 54 are aligned in the general direction of fluid
flow along the upper
surface of the tray deck 26, with the attachment leg 52 located at the
upstream side of the fixed
valve 32. The upstream attachment leg 52 in one embodiment is greater than
that of the
attachment leg 54 to facilitate a more streamlined flow of fluid around the
opening 46.
[00047] The valve cover 50, in one embodiment, is in the form of an isosceles
trapezoid with
the attachment legs 52 and 54 connected to opposed parallel first and second
ends of the valve
cover 50. The valve cover 50 may alternatively be formed with other shapes.
The valve cover
50 is dimensioned to extend outwardly beyond the entire perimeter of the
opening 46 in the tray
deck 26 to more effectively shield the opening 46 against the detrimental
downward weeping of
fluid through the opening 46 and has a downwardly-extending outer perimeter
region 66. The
valve cover 50 (except at the perimeter region 66) lies in a plane that is
parallel to that of the tray
deck 26. In other embodiments, the valve cover 50 may be inclined, such as in
an upward
direction in the general direction of fluid flow on the upper surface of the
tray deck 26.
[00048] The downstream attachment leg 54 in each fixed valve 32 includes a
louvered vent
opening 68 directed in the downstream fluid-flow direction away from the
upstream attachment
leg 52. The vent opening 68 allows fluid ascending through the opening 46 in
the fixed valve 32
to vent through the attachment leg 54 to facilitate intermixing with the fluid
flowing along the
upper surface of the tray deck 26 and to provide a directional push to the
flowing fluid. Each of
the fixed valves 32 on tray deck 28 are of the same construction as those
described above on the
tray deck 26.
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[00049] It has been found through comparative testing that the fixed valves 32
reduce the
entrainment of liquid in the vapor ascending through the fixed valves 32 and
decrease the
weeping of liquid downwardly through the fixed valves 32 in comparison to
conventional
PROVALVE' fixed valves that are of similar construction but lack the
downturned perimeter
region 66 of the valve cover 50, the weir 48 surrounding the opening 46, and
the vent opening 68
formed in the downstream attachment leg 54. The results of the comparative
testing are set forth
in Fig. 21.
[00050] Turning to Figs. 12-20, moveable valves 132 having many of the same
structural
features as fixed valves 32 are illustrated in a tray deck 126. For ease of
reference, the prefix "1"
is used with the reference numerals for components of the moveable valves 132
that generally
correspond to those of the fixed valves 32. The moveable valves 132 each
comprise an opening
146 that extends through the tray deck 126 and a weir 148 extending upwardly
from the tray
deck 126 a preselected distance along an entire perimeter of the opening 146.
[00051] In each fixed valve 132, a valve cover 150 is attached to first and
second attachment
legs 152 and 154. While two attachment legs 152 and 154 are used in the
illustrated
embodiment, additional attachment legs could be used if desired.
[00052] The attachment legs 152 and 154 are located at opposite ends of the
valve cover 150
and extend perpendicularly to the tray deck 126. Each of the attachment legs
152 and 154 has an
upper end that is attached to and is integral with an edge of the valve cover
150. The attachment
legs 152 and 154 extend downwardly through parallel slots 156 and 158 (Fig.
12), respectively,
positioned on opposite sides of the opening 146 in the tray deck 126. Each of
the attachment
legs 152 and 154 includes a locking tab 164 that has an upper surface spaced a
preselected
distance below the valve cover 150. The locking tab 164 engages against an
under surface of
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said tray deck 126 to fix the upper limit of upward movement of the valve
cover 150.
Engagement of the under surface of valve cover 150 on an upper edge of the
weir 48 sets the
lower limit of downward movement of the valve cover 150. Alternatively,
shoulders 160 and
162 such as shoulders 60 and 62 used with attachment legs 52 and 54 described
above may be
used to set the lower limit of downward movement. The distance between the
locking tab 164
and the under surface of the valve cover 150 is selected to set the range of
the vertical distance of
movement of the attachment legs 160 and 162 and the valve cover 150 carried
thereon in
response to variations in upward pressure exerted on the under surface of the
valve cover 150 by
the fluid ascending through the openings 146 in the tray deck 126. For
illustration purposes, the
right-hand moveable valve 132 in Fig. 13 is shown in its fully-open position
and the left-hand
moveable valve 132 in that figure is shown in its closed position.
[00053] The locking tab 164 can be of various suitable forms that allow the
attachments legs
152 and 154 to be inserted downwardly through the slots 156 and 158 as
described above with
reference to locking tab 64.
[00054] Attachment leg 152 has a width that is greater than a largest
corresponding width of
the opening 146 in the tray deck 126 to shield the opening against unwanted
weeping of fluid
downwardly through the opening 146. The moveable valves 132 are oriented on
the tray deck
126 so that the attachment legs 152 and 154 are aligned in the general
direction of fluid flow
along the upper surface of the tray deck 126, with the attachment leg 152
located at the upstream
side of the moveable valve 132. The upstream attachment leg 152 in one
embodiment is greater
than that of the attachment leg 154 to facilitate a more streamlined flow of
fluid around the
opening 146.
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[00055] The valve cover 150, in one embodiment, is in the form of an isosceles
trapezoid with
the attachment legs 152 and 154 connected to the opposed parallel first and
second ends of the
valve cover 150. The valve cover 150 may alternatively be formed with other
shapes. The valve
cover 150 is dimensioned to extend outwardly beyond the entire perimeter of
the opening 146 in
the tray deck 126 to more effectively shield the opening 146 against the
detrimental downward
weeping of fluid through the opening 146 and has a downwardly-extending outer
perimeter
region 166. The valve cover 150 (except at the perimeter region 166) lies in a
plane that is
parallel to that of the tray deck 126. In other embodiments, the valve cover
150 may be inclined,
such as in an upward direction in the general direction of fluid flow on the
upper surface of the
tray deck 126.
[00056] The downstream attachment leg 154 in each moveable valve 132 may
differ from the
downstream attachment leg 54 in the fixed valve 32 by omitting the louvered
vent opening 68 or
substituting a simple opening in place of the louvered vent opening 68.
Alternatively, a louvered
vent opening 68 may be included, such as in an embodiment in which the
shoulders described
above are used to set the lower limit of the downward movement of the valve
cover 150. In such
an embodiment, the louvered vent opening would be positioned above the
shoulders so that it
does not impede the downward movement of the attachment leg 154 in its
associated slot 158.
[00057] From the foregoing, it will be seen that this invention is one well
adapted to attain all
the ends and objectives hereinabove set forth together with other advantages
that are inherent to
the structure.
[00058] It will be understood that certain features and subcombinations are of
utility and may
be employed without reference to other features and subcombinations. This is
contemplated by
and is within the scope of the invention.
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[00059] Since many possible embodiments may be made of the invention without
departing
from the scope thereof, it is to be understood that all matter herein set
forth or shown in the
accompanying drawings is to be interpreted as illustrative and not in a
limiting sense.
